Visible light communication is a new short-distance wireless high-speed communication technology developed from Light Emitting Diode (LED) and other technologies, and operates under such a principle that a high-speed binary signal is emitted by a light source flickering at a high frequency because the LED or the like can be lighten or blacked out rapidly, and the binary signal is received and converted by a corresponding device into an electric signal from which information is obtained.
Particularly the visible light communication is advantageous in that it has better directivity than radio communication because electromagnetic radiation is not generated in a large space; and also since it is difficult for the signal transmitted by the transmitter to be captured in another direction than the receiver, the visible light communication also has good confidentiality. Moreover since the transmitting device (e.g., an LED light emitting device, etc.) and the receiving device (e.g., an photosensitive device, etc.) required for the visible light communication are less expensive than devices used in the radio communication, the visible light communication can be widely popularized and applied.
However in the existing visible light communication system typically the output voltage of the photoelectric conversion device is compared by a differential amplification circuit with constant voltage to output a level signal, so that an inversion condition of the output level may be significantly affected by ambient light. For example, if the ambient light is bright so that the voltage signal output as a result of conversion by the photoelectric conversion device when the visible light emitting device is either lightened or blacked out is above the other given constant reference voltage, or if the ambient light is dark so that the voltage signal output as a result of conversion when the visible light emitting device is either lightened or blacked out is below the other given constant reference voltage, then the output level of the differential amplification circuit can not be inverted when the visible light emitting device is either lightened or blacked out, so the visible light signal fails to be received and converted, so that the visible light communication system requires the light environment as a whole to be highly satisfactory, and if the light source in the environment is not satisfactory, then the communication system will have a high bit error rate, a poor quality of communication and even can not operate.